Mapping Fractures by Imaging Passive Seismic Emissions for Ambient Listening Before Drilling and for Frac Monitoring Charles Sicking*, Alfred Lacazette, Jan Vermilye, Peter Geiser, Global Microseismic Services Summary Knowledge of faults or fracture zones prior to any drilling offers substantial benefits for all phases of operations from exploration to development planning and hydraulic fracture design. We describe the application of a relatively new passive-seismic method that produces images of seismic activity that result from movements on discrete features such as faults and fractures prior to drilling. We will present data acquired with passive seismic listening arrays for unconventional reservoirs and a fractured carbonate reservoir before any drilling. For frac monitoring, microseismic recordings are used to directly image the fracture networks that are activated by the pressure changes caused by the frac pumping, by earth tides and by other mechanisms. Fracture networks that are interconnected to form transmissive fracture fairways can carry pressure from the hydraulic fracturing (frac) point to locations that can be great distances from the well. Animations and slides are used to show examples of seismic emission activity continuously through time. These graphics show the intensity of induced fracturing, formation breakdown, and natural fracture activity as a function of time while the pumping for the fracing is occurring. Examples show the timing of when fractures open away from the perf location for the stage being pumped, the time of fractures that open along paths that intersect adjacent wells, and the rock movement along preexisting fractures. Examples are presented of fracture images for ambient listening before drilling and for frac monitoring. Introduction This work describes a new passive-seismic method that images subsurface fracture networks that are likely to be hydraulically transmissive prior to drilling. The data required can be obtained inexpensively by listening to ambient seismic emissions during standard 3D reflection surveys during times when shooting or vibrating is not in progress. The resulting images allow potential sweet spots to be targeted with the first well and allow field development planning to begin before beginning a drilling campaign. Ambient images can also aid in planning hydraulic fracture treatments. More complete TFIs are obtained when monitoring a fracture treatment because the fluid pressure pulse and poroelastic stress changes produced by the frac illuminate the transmissive fracture fairways over a large area and provide more energy for imaging. However, many features that are illuminated by fracture treatments appear in the ambient, pre-frac images. Passive emission volumes and Tomographic Fracture Images (TFI TM ) are computed from microseismic trace data collected using either a surface array or a buried array. The field records are processed to show cumulative seismic activity per voxel for long time windows (Geiser et al, 2006; Dricker et al 2010; Shkarin et al, 2010). All passive signals arriving at the receiver array from the target depth are integrated. This includes micro-earthquakes (MEQs) and signals from Long-Period, Long-Duration events (LPLDs). The method captures a greater fraction of the available seismic energy than conventional MEQ-based microseismic methods and can distinguish between transmissive and non-transmissive fractures. More energy is captured for two reasons: 1. Conventional MEQ methods work only with events that are sufficiently large to be distinguished as MEQs. Small MEQs are many orders of magnitude more abundant than large ones and are not pickable. Hence there is more total energy in small, non-pickable events than in the small number of distinguishable large events. TFI captures the energy from large and small MEQs. 2. TFI captures the energy of Long-Period, Long-Duration (LPLD) events, which are low-frequency rumbles that can continue for seconds, minutes, or longer and do not have distinct first arrivals. Recent research (Das and Zoback, 2011; Zoback et al, 2012) indicates that LPLDs are probably the most important indicator of hydraulic fracture stimulation. LPLDs cannot be picked as distinct events, and therefore are invisible to conventional MEQ microseismic methods. TFI captures LPLD energy. The integration of all seismic emissions captures a much greater fraction of the energy generated during fracing than MEQ methods. Fracture Imaging workflow and Method The processing of microseismic trace data for imaging fracture networks includes several steps: geometry, velocity and statics calibration, noise filtering, semblance computation, coherence and energy extraction, and computation of fracture surfaces. Figure 1 shows a screen grab of the interactive tool that is used for velocity and statics calibration. The near surface velocity used for elevation statics and the residual statics can be changed interactively to find the optimum focusing. The velocity model is changed interactively to focus the perf shots to the known depth and X, Y locations. DOI http://dx.doi.org/10.1190/segam2013-1469.1 © 2013 SEG SEG Houston 2013 Annual Meeting Page 5131 Downloaded 02/25/23 to 71.56.200.82. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/page/policies/terms DOI:10.1190/segam2013-1469.1